Men between 30 and 65 years of age who have had moderate to severe chronic pain due to osteoarthritis for at least 3 months and healthy, pain-free men in the same age range may be eligible for this study. Patients taking an opioid-based medication such as percocet, vicodin, or morphine for pain relief, as well as patients who are not taking opioids, may participate. Candidates are screened with a medical history, physical examination, blood tests, including a blood test to look for possible "pain genes," electrocardiogram, x-ray, and questionnaires that assess the impact of pain on functional level and psychological well being.